The present invention relates to a thermally printing apparatus for printing on a sheet of paper via a thermal ribbon having a thermally transferable ink layer, which has a thermal print head including heat generating elements which are held in pressed contact with the surface of the sheet of paper via the thermal ribbon and which are selectively energized to apply heat to the ink layer of the thermal ribbon to fuse the ink for adherence of the fused ink to the surface of the paper to print characters, symbols, graphical representations, etc.
In a commonly known thermally printing apparatus constructed as shown in FIG. 11, a printing operation is achieved by pressing a thermal print head 108, via a thermal ribbon 112, against a relatively uneven surface of a sheet of paper 114 set on a platen 113. When heat is generated by heat generating elements 108a at a front end portion of the thermal print head 108, an ink 112b on the thermal ribbon 112 is fused and adheres to the surface of the paper 114. After the thermal ribbon 112 is pulled via a separating roller 116 and separated from the paper 114, layers of the ink are transferred to the paper 114, as indicated at a, b, c, d and e in FIG. 17. In such a thermal printer, the use of a sheet of paper having an unsmooth or uneven printing surface will lead to application of a thin ink as seen at b or partial application of the ink as shown at c due to the roughness or unevenness of the surface, resulting in reduced printing density, unevenly or partially printed characters and figures, and other defects. Consequently, the print quality on the paper 114 will be reduced as a whole.